1. Field
Exemplary embodiments relate to a variable-bandwidth adaptive notch filter, and a method and apparatus for canceling howling by using the variable-bandwidth adaptive notch filter, and more particularly, to a variable-bandwidth adaptive notch filter which cancels howling with a bandwidth varying according to a howling frequency by using a frequency warping technique, and a method and apparatus for canceling howling by using the variable-bandwidth adaptive notch filter.
2. Description of the Related Art
Low-frequency oscillation sound, called “howling”, is generated during a procedure where sound or vibration at an output side (a speaker or a receiver) is fed back to an input side and amplified at the input side and the output sound or vibration is fed back to the input side and amplified again at the input side in a public address system or a record player. When howling, which is sound generated when micro sound or vibration is fed back in a speaker, is generated, a device enters a maximum power state in an instant, thereby damaging an audio system of the device.
To cancel howling, which involves resonance and oscillation of a particular frequency, the particular frequency is found and attenuated.
In general, an equalizer is used to attenuate a particular frequency. To cancel howling by using an equalizer, a graphic equalizer is adjusted to be flat, a non-directional microphone having a flat feature is connected, and an observation is made about in which frequency band howling is generated with an increase in a gain of a system. If the frequency band where howling is generated is determined, a process of pulling down an equalizer slider of the frequency band is repeated until a sufficient sound reinforcement gain is obtained. In this way, a maximum stable gain, which prevents howling, can be obtained.
However, in this method, tone changes due to a large change of frequency characteristics. Moreover, as a frequency band, which causes howling, changes with a position of an audio system, continuous adjustment is required in association with the change. Since a howling cancellation frequency bandwidth is fixed, a speech component may also be removed together with howling in a low-frequency band where the speech component is present.